1. Field of the Invention
The invention relates to a high-frequency circuit having a function of switching a band in a plurality of circuit blocks each of which deals with a high-frequency signal.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a conventional high-frequency circuit 40 for driving one of bands in a power amplifier which accomplishes a dual-band power amplification module.
The illustrated high-frequency circuit 40 is comprised of a main transistor 50, a bias circuit 51 which supplies a current to a base of the main transistor 50, a band-switching circuit 52 for switching a band, and a gain control circuit 53.
The main transistor 50 is electrically connected through a collector thereof to a power source voltage terminal Vcc through which a power source voltage is supplied, and further electrically connected through a base thereof to an input terminal Vin through which a high-frequency signal is input.
The bias circuit 51 is comprised of a first transistor 54, a second transistor 55, and a first resistor 56.
The first transistor 54 is electrically connected through a collector thereof to the power source voltage terminal Vcc, and further electrically connected through an emitter thereof to both a base of the main transistor 50 and a base of the second transistor 55.
The second transistor 55 is electrically connected through a collector thereof to the power source voltage terminal Vcc through the first resistor 56, and further electrically connected through a base thereof to both a base of the main transistor 50 and an emitter of the first transistor 54.
The band-switching circuit 52 is comprised of a third transistor 57, a fourth transistor 58, a fifth transistor 59, a second resistor 60, a third resistor 61, and a fourth resistor 62.
The third transistor 57 is electrically connected through a base thereof to a band-switching voltage terminal Vsw through which a band-switching voltage is supplied, through the second resistor 60, and further electrically connected through a collector thereof to the power source voltage terminal Vcc through the third resistor 61.
The fourth transistor 58 is electrically connected through a base thereof to a node D at which a collector of the third transistor 57 and the third resistor 61 are electrically connected to each other, and further electrically connected through a collector thereof to the power source voltage terminal Vcc through the fourth resistor 62.
The fifth transistor 59 is electrically connected through a base thereof to a node at which a collector of the fourth transistor 58 and the fourth resistor 62 are electrically connected to each other, and further electrically connected through a collector thereof to a node at which a collector of the second transistor 55 and the first resistor 56 are electrically connected to each other.
The gain control circuit 53 is electrically connected to a gain control voltage terminal Vagc through which a gain control voltage is supplied, and further electrically connected to a node C at which a collector of the fifth transistor 59 and a node at which a collector of the second transistor 55 and the first resistor 56 are electrically connected to each other are electrically connected to each other.
In the conventional high-frequency circuit 40 illustrated in FIG. 1, a gain of the main transistor 50 is controlled by the gain control circuit 53, and a band is switched when a band-switching voltage supplied through the band-switching voltage terminal Vsw is changed between high and low levels. Specifically, a band is turned off when a reference current I1 running through the bias circuit 51 runs through the fifth transistor 59 as a current I2, whereas a band is turned off when a path through which the current I2 runs is interrupted. Thus, a band is switched on or off by allowing the reference current I1 to run through a path or interrupting the path.
The conventional high-frequency circuit 40 illustrated in FIG. 1, for instance, receives a plurality of high-frequency signals which are identical with one another or different from one another, and then, amplifies each of the received high-frequency signals, or converts frequencies of the received high-frequency signals.
A high-frequency circuit such as one illustrated in FIG. 1 is presently frequently used in a mobile communication device such as a cellular phone.
It is quite important for a cellular phone driven by a battery arranged therein, to be fabricated in a smaller size and designed to be driven with smaller power consumption.
To this end, the high-frequency circuit 40 illustrated in FIG. 1 is required to reduce a current running through the power source voltage terminal Vcc down to a range of about 10 to about 30 xcexcA when the gain control voltage is lowered to 0.1V. A smaller current running through the power source voltage terminal Vcc is more preferable, since the current defines a period of time in which a battery arranged in a cellular phone can work.
However, a band in the conventional high-frequency circuit 40 illustrated in FIG. 1 was switched merely by converting a direction in which the reference current I1 ran, and accordingly, it was not possible in the conventional high-frequency circuit 40 to reduce a current running through the power supply voltage terminal Vcc when a gain control voltage was set at 0.1V.
Japanese Unexamined Patent Publication No. 10-65466, which is based on the U.S. patent application Ser. No. 08/664,972 filed on Jun. 3, 1996, has suggested an amplifier for amplifying a signal having one of predetermined frequencies. The suggested amplifier is comprised of a plurality of amplifying units each of which operates under one of the predetermined frequencies, and a controller which allows one of amplifying units to operate in accordance with one of the predetermined frequencies, and disallows the rest of the amplifying units to operate.
Japanese Unexamined Patent Publication No. 10-313259 has suggested a high-frequency circuit comprised of a plurality of circuit blocks into which received radio-frequency signals are input. Each of the circuit blocks includes a DC switching transistor which interrupts a current path through which a dc bias current runs in a circuit block in accordance with a received signal indicating that the circuit block is not selected.
The above-mentioned problem remains unsolved even in the above-identified Publications.
In view of the above-mentioned problems in the conventional high-frequency circuits, it is an object of the present invention to provide a high-frequency circuit which is capable of reducing a current running through a power supply voltage terminal down to tens of microamperes (xcexc A), even if a gain control voltage is relatively low, for instance, at about 0.1V.
The present invention provides a high-frequency circuit having a function of switching a band in a bias circuit of a power amplifier module, used in a dual mode, and accomplishing band-switching without an increase in a circuit current when a power amplifier is off.
There is provided a high-frequency circuit including (a) a bias circuit to which a gain control voltage is input and which controls gains of transistors arranged in the bias circuit in accordance with the gain control voltage, and (b) a band-switching circuit which switches a band and through which a reference current runs, wherein the band-switching circuit includes a transistor which cuts off a current path through which the reference current runs, in synchronization with the gain control voltage.
There is provided a high-frequency circuit including (a) a bias circuit to which a gain control voltage is input and which controls gains of transistors arranged in the bias circuit in accordance with the gain control voltage, and (b) a band-switching circuit which switches a band and through which a reference current runs, wherein the band-switching circuit includes two transistors electrically connected in cascode to each other, one of the two transistors which is located downstream of the other has a gate electrically connected to a gain control voltage terminal through which the gain control voltage is input, and each of the two transistors is comprised of a complete enhancement mode field effect transistor.
There is provided a high-frequency circuit including (a) a bias circuit to which a gain control voltage is input and which controls gains of transistors arranged in the bias circuit in accordance with the gain control voltage, and (b) a band-switching circuit which switches a band and through which a reference current runs, wherein the bias circuit includes at least one pair of transistors and a band-switching transistor used for switching a band, the band-switching transistor is electrically connected in series to a line through which the gain control voltage is supplied, and the gain control voltage is applied to the pair of transistors through the band-switching transistor.
The bias circuit may be designed to include at least one pair of transistors and a band-switching transistor used for switching a band, in which case, the band-switching transistor is electrically connected in series to a line through which the gain control voltage is supplied, and the gain control voltage is applied to the pair of transistors through the band-switching transistor.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
The high-frequency circuit in accordance with the present invention makes it possible to reduce a current running through a power supply voltage terminal down to tens of microamperes (xcexcA), even if a gain control voltage is relatively low, for instance, at about 0.1V.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.